P0620
Generator Control Circuit
- Severity
- High
- Driving
- Drivable — book it in
A fault in the generator control circuit - the circuit the control module uses to tell the alternator how much to charge. On modern vehicles the alternator is not self-regulating; the module varies charging to suit the battery's state, engine load and fuel economy. Without that control the alternator may charge too much, too little, or not at all.
Possible causes
- CommonWiring or connector fault between the module and the alternator
- CommonFailed alternator regulator
- CommonCorroded connector at the alternator - it sits in a hot, dirty place
- PossibleChafed harness near the engine
- PossibleAftermarket or wrong-specification alternator that does not support the control protocol
- RareFailed control module driver
What you might notice
- Battery warning light on
- Charging voltage too high or too low
- Battery going flat, or being overcharged
- Lights dimming or unusually bright
- Check engine light on
What to check, in order
- Measure charging voltage at the battery and see which way it is wrong. That tells you whether the fault has left the alternator at full output or at none.
- Inspect the connector at the alternator for corrosion and heat damage.
- Check the wiring between the module and the alternator for chafing.
- Ask whether the alternator has been replaced. A unit that does not support the vehicle's control protocol sets this code even though it charges.
- Check the earth connections at the alternator and engine.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Computer output circuits and control module
P0600P0601P0602P0603P0604P0605P0606P0607P0608P0609P0610P0611P0612P0613P0614P0615P0616P0617P0618P0619P0620P0621P0622P0623P0624P0625P0626P0627P0628P0629P0630P0631P0632P0633P0634P0635P0636P0637P0638P0639P0640P0641P0642P0643P0644P0645P0646P0647P0648P0649P0650P0651P0652P0653P0654P0655P0656P0657P0658P0659P0660P0661P0662P0663P0664P0665P0666P0667P0668P0669P0670P0671P0672P0673P0674P0675P0676P0677P0678P0679P0680P0681P0682P0683P0684P0685P0686P0687P0688P0689P0690P0691P0692P0693P0694P0695P0696P0697P0698P0699